The right-back was omitted from Steve Clarke's squad for the visit of Middlesbrough on Saturday and underwent a medical in south London today, before putting pen-to-paper.

Cummings joined Reading in 2009 from Chelsea but has found first-team action hard to come by, making just 77 league appearances for the Royals.

The Jamaican international played just five league games this season, with his cameo from the bench against Brighton on Boxing Day his final appearance in a Reading shirt.

Cummings notched just one goal for the Royals, a 25-yard effort against Wigan Athletic on the opening day of this campaign.

Following the move, Nick Hammond said: "“Shaun has been an excellent professional, very reliable and he made a real contribution to the club - particularly when he started more than 30 games in the promotion season – so we all wish him well for the future.”

It won't be long until Reading fans see Cummings in action again as the Royals travel to the New Den for a rearranged league fixture on Tuesday, January 27.

"This is a very good club and that is why I came here," the defender told the Millwall FC website. "I'm very pleased to be here.

"The position in the League isn't where we should be so hopefully as a club can step on. It is going to be an important time between now and the end of the season in getting the club out of the zone it is in and progressing forward.

"From a personal point of view I want to hit the ground running straight away and play how I know I can play.

"I'm a hard worker and I never like to lose. I like to get forward and get crosses in but as a defender I also want to keep clean sheets and do well in my one-on-one duels."